Certain statics/objects causing graphics lag?

[SchildVogel]

I've noticed that on a lot of maps, I only get "graphics lag" when looking in different directions depending on where I am on the map. I get no "lag" at all when looking straight up or down. I assume this is because certain buildings/objects on the map require more cpu power to render, or something? The size of the map doesn't matter at all, because I can play on Yamalia, Kashan, and Qin Ling with generally no problems, but relatively small maps like Gaza can drive me insane. I believe the biggest problems are tunnel systems, apartment-type buildings, mosques, and objects on fire.

I guess I'm mainly just wondering which map objects are most likely causing this. Whether that's higher poly/tri counts, or whatever.

side note: I am in the process of defragging/cleaning my comp and will eventually get a completely new system, which will solve the problem.

system:
Intel Pentium 4 3.20GHz
2GB RAM
GeForce 7600 GS 512MB